Examples of an ionization analysis method and apparatus utilizing barrier discharge are described in the following literature:
1. Na Na, Chao Zhang, Mengxia Zhao, Sichun Zhang, Chengdui Yang, Xiang Fang and Xinrong Zhang, “Direct detection of explosives on solid surfaces by mass spectrometry with an ambient ion source based on dielectric barrier discharge”, J. Mass Spectrom. 2007; 42:1079-1085
2. Na Na, Mengxia Zhao, Sichun Zhang, Chengdui Yang and Xinrong Zhang, “Development of a Dielectric Barrier Discharge Ion Source for Ambient Mass Spectrometry”, J Am Soc Mass Spectrom. 2007, 18, 1859-1862
The ion analysis method and apparatus described in these references have a plate-shaped electrode, a glass plate placed on the surface of the plate-shaped electrode and a needle-shaped electrode disposed substantially perpendicular to the surface of the glass plate (the plate-shaped electrode) and spaced away from the glass plate, and impress an alternating high-voltage across the plate-shaped electrode and needle-shaped electrode and induce a barrier discharge. A sample serving as an object to undergo analysis is placed on the glass plate and is exposed to a plasma torch produced by the barrier discharge. As a result, atoms and molecules are desorbed from the sample and ionized. The ions are introduced to a mass analyzer and analyzed.
Since a sample is exposed directly to a plasma torch (non-equilibrium plasma) produced by barrier discharge in the ion analysis method and apparatus described in the references cited above, decomposition of the sample itself by high-energy electrons in the plasma, decomposition of molecules desorbed from the sample and ionized, and polymerization of fragment ions produced by decomposition and the like occur. A problem, therefore, is that there are cases where accurate analysis cannot always be achieved.